Subharmonic image rejection and image enhancement mixer

A frequency mixer for combining an input signal with a local oscillator frequency to obtain an intermediate frequency, the input signal having at least a desired frequency and an image frequency, the desired frequency and the image frequency being offset from a multiple n of the local oscillator frequency by the intermediate frequency, comprising:

• a power divider having and input for receiving the local oscillator frequency, a first output, and a second output;
• a phase shifter for delaying the local oscillator frequency by (90.degree./n) having an input coupled to the first output of the power divider and an output, n being greater than 1;
• input means for applying the input signal to a first and a second subharmonic mixer and for reflecting a self-generated image signal into one of said first and second subharmonic mixers, said input means having a first output arm and a second output arm;
• said first subharmonic mixer having a first local oscillator input coupled to the second output of said power divider, a first input signal input coupled to the first output arm of said input means, and a first mixer output, the first subharmonic mixer producing the intermediate frequency at the first mixer output, said intermediate frequency including a first desired component and a first image component;
• said second subharmonic mixer having a second local oscillator input coupled to the output of said phase shifter, a second input signal input coupled to the second output arm of said input means, and a second mixer output, the second subharmonic mixer producing the intermediate frequency at the second mixer output, said intermediate frequency including a second desired component and a second image component;
• and
• a quadrature hybrid having a first input coupled to the output of said first subharmonic mixer, a second input coupled to the output of said second subharmonic mixer, a first output, and a second output, the quadrature hybrid producing a sum of said first desired component and said second desired component at the first output and a sum of said first image component and said second image component at the second output;
• wherein the first and second subharmonic mixers further comprise an anti-parallel diode pair for mixing the local oscillator frequency and the input signal, a coupled line filter for passing the input signal, a short circuit stub for passing the local oscillator frequency, a first open stub for rejecting the input signal and passing the intermediate frequency, a second open stub for passing the intermediate frequency, and a radial stub for terminating a sum frequency.